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MXene-based nanozymes have increased research enthusiasm in the field of food safety and environment monitoring. Herein, the Cu NCs/Ti

A facile method for fabricating polymer carbon dots (PCDs) with characteristic dual-emission at 570 and 620 nm by 1,8-naphthalenediol in n-propanol solvents was designed. The synthesised PCDs possessed fluorescence enhancement performance toward the water in organic solvents. Based on this peculiar phenomenon, a highly efficient fluorescent probe for water detection in organic solvents such as N,N-dimethylformamide, dimethyl sulfoxide and n-propanol was established with a wide detection range from 0 to 50%. The probe can also be utilised to determine water content in other organic solvents. The practical application was explored by studying the response of PCDs toward the water in various spirit samples. This method may offer a new way of detecting water in organic solvents by PCDs.

In this work, we developed a ’’naked-eye’’ colorimetric and ratiometric fluorescence probe for a very important biomarker of uric acid (UA). The method was based on the oxidation of UA by uricase to allantoin and hydrogen peroxide, and then o-Phenylenediamine (OPD) was oxidized to the yellow-colored 2,3-diaminophenazine (oxOPD) in the presence of horseradish peroxidase (HRP) and hydrogen peroxide. The fluorescence emission of glutathione functionalized Ti3C2 MQDs (GSH-Ti3C2 MQDs) centered at 430 nm overlaps with the UV absorption of oxOPD at 425 nm to a large extent, which facilitates fluorescence resonance energy transfer (FRET) between GSH-Ti3C2 MQDs and oxOPD. With the increase of the UA concentration, the emission at 430 nm of GSH-Ti3C2 MQDs is progressively quenched and the emission at 568 nm of oxOPD was gradually increased. Moreover, the probe we designed is easier to distinguish with color change by naked eye for the detection of UA. This is the first report about the determination of UA by a ’’naked-eye’’ colorimetric and ratiometric fluorescence method combining GSH-Ti3C2 MQDs and uricase/HRP enzymes. This work enables assays to perform fluorescence and visual detection of biomarker in biological fluids based on Ti3C2 MQDs.

A ratio fluorescence nanoprobe was constructed by simple mixing BCNO QDs with 8-hydroxyquinoline-5-sulfonic acid (HQSA), which had an obvious fluorescence peak at 420 nm and a weak fluorescence peak at 500 nm, corresponding to the BCNO QDs and HQSA, respectively. This fluorescence probe takes stable fluorescence of BCNO QDs as an internal standard, based on HQSA chelating enhanced fluorescence and specificity of phosphate in the presence of Mg

A miniature device was design for the point-of-care testing (POCT) of tetracycline (TC) including a ratio fluorescence test strip, a sample slot, a UV lamp and a smartphone. The nitrogen and sulfur co-doped carbon dots (N, S-CDs) and Eu

A novel colorimetric and ratiometric fluorescence sensor has been established based on boron carbon oxynitride quantum dots (BCNO QDs) and Ca

Ti3C2 MQDs were synthesized using an effective fluorine-free method with excitation/emission maxima at 390/490 nm and a fluorescence quantum yield of 11.78%. In contrast to the traditional, hazardous, and time-consuming process of HF pretreatment, our fluorine-free method is safe and simple. Acetylcholinesterase (AChE) could catalyze the hydrolysis of acetylthiocholine (ATCh) to produce thiocholine which was further reacted with Ehrman's reagent and decomposed to form a yellow product 2-nitro-5-thiobenate anion (TNB). Due to the obvious overlap between the excitation spectrum of Ti3C2 MQDs and the absorption spectrum of TNB, AChE catalyzed the hydrolysis of substrate DTNB/ATCh to form TNB, which can effectively quench the fluorescence of Ti3C2 MQDs through the inner filter effect (IFE). However, the presence of organophosphorus (OPs) inhibited the activity of AChE, leading to a less expressed IFE and increasing recovery of fluorescence. This was used for the quantification of OPs with a detection limit of 0.20 μg·L-1. Moreover, with the constant increase of AChE activity, the color of the reaction system changed visibly from colorless to yellow, and then from yellow to colorless with further continuous addition of OPs. A colorimetric detection with a paper-based sensor of AChE activity and OP concentration was also fabricated by analyzing changes in RGB value using a smartphone APP. In this work, we proposed an effective fluorescence/colorimetric two-mode detection method, which opened a new horizon to detect other targets.

The Ti3C2 MXene quantum dots (Ti3C2 MQDs) derived from Ti3C2 MXene have received much attention because of their remarkable advantages in biosensing. Nevertheless, the functionalization of Ti3C2 MQDs to improve their properties is just in its infant stage. Herein, we firstly synthesized nitrogen and boron co-doped Ti3C2 MQDs (N, B-Ti3C2 MQDs) with good water solubility, strong stability, and high optical characteristics. The N, B-Ti3C2 MQDs exhibit excitation wavelength-dependent blue photoluminescence with optimal excitation/emission peaks at 335/439 nm. Nowadays, the development of fast and real-time detection of tetracycline (TC) in animal derived food is very essential. In this work, a novel point-of-care testing (POCT) platform was established based on ratiometric fluorescence method using N, B-Ti3C2 MQDs coupled with Eu3+. Upon addition of TC in the Eu3+/N, B-MQDs system, blue fluorescence emission of N, B-Ti3C2 MQDs was quenched and red fluorescence emission of Eu3+ was enhanced gradually, which was ascribed to the synergistic inner filter effect and antenna effect. Moreover, we prepared test papers with N, B-Ti3C2 MQDs and Eu3+ for TC detection based on the change of fluorescence color, which could be recognized by color recognizer app installed in the smartphone. Therefore, great promise for POCT of TC is given with the merits of simplicity and visible detection possibility. The proposed method demonstrated a low detection limit of 20 nM. Application of the platform for TC quantification in milk samples opened a novel means for the potential use of N, B-Ti3C2 MQDs in food safety.

In this work, we have developed a near-infrared emissive polyethyleneimine capped Ag2(PEI-Ag2S QD) quantum dots based chemosensor for sensing trace-level Hg2+ in water by taking advantage of the metal-induced aggregation strategy. The fluorescence determination of Hg2+ by PEI-Ag2S QD at different pH (pH 4, 7, and 10) were performed, respectively. Under the optimum conditions, the selectivity of this system for Hg2+ over other metal ions in aqueous solutions was remarkably high, and its detection limits was 0.5 nM at pH 4. In addition, the present approach provides the advantages of rapidity, simplicity, low background and low cost. The assay also offers great potential for specific detection of Hg2+ in real water samples. This developed PEI-Ag2S QD-based method presages more opportunities for application in environmental systems.

This work has assembled ZnSe:Mn/ZnS quantum dots (QDs)-monoclonal anti-microcystin-Leucine Arginine (anti-MC-LR) antibody bioconjugates as a room temperature phosphorescence (RTP) probe using 1-ethyl-3-(3-dimethyllaminopropyl) carbodiimide/N-Hydroxysuccinimide chemistry for detecting MC-LR. Once the specific interactions occurred between these MCs and their antibodies on the surface of ZnSe:Mn/ZnS QDs, the RTP of ZnSe:Mn/ZnS QDs was quenched with the increased concentration of MC-LR. Under the optimised conditions, the linear range of MC-LR was determined to be 0.9–8.8 nM. The linear relationship between (P 0–P)/P 0 and concentration of MC-LR were observed with the regression equation (P 0–P)/P 0 = 0.03908C + 0.0456 with the detection limit of 0.038 nM. The developed RTP immunoassay favoured environmental applications since the interference from autofluorescence and scattering light was greatly eliminated.

We fabricated a new and selective fluorescent sensor for the detection of citrate by employing g-C3N4 quantum dots (g-CNQDs) and MgFe layered double hydroxide (MgFe-LDH). The g-CNQDs interacted with MgFe-LDH via electrostatic interaction and the fluorescence of g-CNQDs was effectively quenched by MgFe-LDH due to inner filter effect. Upon addition of citrate, the fluorescence of the g-CNQDs was significantly enhanced, arising from the replacement of g-CNQDs by citrate because citrate competed with g-CNQDs to form more stable complexes with MgFe-LDH. Therefore, we developed a “turn-off–on” fluorescence assay method for the detection of citrate. This method enabled the selective detection of citrate with linear range of 0.5–3.0 μM and 3.0–10.0 μM with a 12.3 nM limit of detection. This method exhibited advantages including easy preparation, environmentally friendly process and rapid response toward citrate.

Carbon nitride quantum dots (CNQDs) were embedded in the sodium carboxymethyl cellulose (CMC) matrix to form CNQDs-CMC film to explore the room temperature phosphorescence (RTP) of CNQDs, which suppress the non-radiative relaxation process due to the internal hydrogen bonding interactions between CMC and CNQDs. Then, a simple, inexpensive, background-free miniature device integrating with CNQDs-CMC film and smartphone was fabricated for rapid and quantitative detection of melamine (MEL). In the present of MEL, the yellow RTP color of the CNQDs-CMC film was quenched and photographed by the smartphone. The Color Recognizer APP in the smartphone recognized the red (R) value for quantitative detection of MEL. Thus, digital image colorimetry (DIC) determination of MEL was achieved due to the visible RTP color change of CNQDs-CMC film. The smartphone-based miniature device provided a promising platform for the on-site monitoring analytes in the complex matrix including food safety, environmental screening, health monitoring, and disease prevention.

Ti

The Ti

Green emitting copper nanoclusters (G-Cu NCs), yellow emitting Cu NCs (Y-Cu NCs), orange emitting Cu NCs (O-Cu NCs) and red emitting Cu NCs (R-Cu NCs) were prepared using chicken egg white as the stabilizer by changing the reaction conditions. This is a green, facile and cheap method to explore different color emitting CuNCs by the same precursor and stabilizers. The G-Cu NCs were employed for the detection of ethanol due to their aggregation induced emission enhancement (AIEE) effect. The fluorescence emission of Cu NCs at 526 nm under the excitation of 444 nm can be effectively enhanced in the presence of ethanol due to AIEE effect, thus realizing the quantitative determination of ethanol content in the range 5–60%. In addition, a visual dual-emission fluorescence probe with the combination of G-Cu NCs and silicon nanoparticles (Si NPs/G-Cu NCs) was designed to evaluate ethanol content conveniently and rapidly. Desirable linear relationship is observed between ratio of fluorescence intensity (I525/I441) and ethanol content under the excitation of 383 nm. Visible color transformation of this probe is observed in the ethanol content range 2–20%. Moreover, the ethanol sensing platforms were applied to the detection and evaluation of the alcohol content of liquor, and the recoveries in liquor were in the range 99.7% to 113%, broadening the applications of Cu NCs and providing a sensitive detection method for ethanol.

A dual-channel "naked-eye" colorimetric and ratio fluorescent probe has been developed based on titanium carbide quantum dots for the detection of curcumin and hypochlorite (ClO

This work integrated zero-valent copper (ZVC) onto the surface of zeolitic imidazolate framework (ZIF) to form hybrids of ZVC/ZIF-8 as a non-noble catalyst for catalytic reduction of PNP as a reliable model reaction. The ZVC/ZIF-8 exhibited superior catalytic properties and good recyclability after the fabrication. 6%ZVC/ZIF-8 hybrids complete the reduction process in 2 min with a rate constant estimated to be 2.39 min -1 . The study's findings explored a simple and powerful way to incorporate metal ions into the backbones of open framework materials without losing their properties.

In this work, 3-aminophenylboronic acid was used as the starting materials to construct boron and nitrogen co-doped carbon dots with tunable dual-emission intensity at 420 and 540 nm with different excitation at 360 and 500 nm, respectively. The dual-emission carbon dots sensor is employed for rapid and sensitive fluorescence-enhancing detection of Pb 2+ . Compared with previous reported methods, their method showed better linear ranges or detection limits. Under the optimal conditions, the limit of detection of 0.9 nM for Pb 2+ was reached with a wide range of 9 nM to 438 μM. The authors believe that the established method has more opportunities for application for other environmental targets.

The work develops a novel method for the detection of bisphenol A (BPA) based on glutathione (GSH)-protected silver sulphide quantum dots (Ag2S QDs), which was simple, fast, non-toxic, sensitive and selective. Ag2S QDs were synthesised with a sulphur–hydrazine hydrate complex as the S2− source and GSH as the stabiliser. Ag2S QDs, near-infrared QDs, offered the advantages over lower background fluorescence and lower signal loss. The fluorescence peak of Ag2S QDs at 650 nm was quenched significantly in the presence of BPA. Good linear correlations were obtained over the concentration range from 0 to 60 μM of BPA under optimised conditions. The developed selective and sensitive method presaged more opportunities for the application in environmental samples.

The rGO–ZnO–Fe3O4 nanocomposites were synthesized by a simple, economical and environmentally benign solvothermal method. The morphology, structure and photocatalytic activity of rGO–ZnO–Fe3O4 nanocomposites were characterized, and the effects of the preparation conditions were analyzed. The 25 mg of rGO–ZnO–Fe3O4 nanocomposites performed efficient photocatalytic activity for the degradation of 25 mL of 4.79 mg/L Rhodamine B under both ultraviolet and visible light irradiation. The nanocomposites could be easily retrieved from the wastewater by extra magnetic field due to the presence of magnetic Fe3O4 nanoparticles. After the degradation experiment was carried out five times, the degradation ratio is still close to 90% after irradiation after 5 cyclic, indicating that the rGO–ZnO–Fe3O4 nanocomposites have high stability for reuse. Therefore, the prepared rGO–ZnO–Fe3O4 nanocomposites may be a promising potential material for wastewater treatment.

Doping is recognized as a powerful way to tailor the defect in the surface and modify the properties of Carbon-based (C-based) materials. Various state-of-the-art techniques have been proposed to prepare boron and nitrogen co-doped C-based materials. Here we first introduced 3-aminophenylboronic acid (APBA) as the single starting material to fabricate boron and nitrogen co-doped carbon dots (N/B-CDs) with high quantum yield (25.9%) through one-pot hydrothermal method without further passivation. We applied the as-prepared N/B-CDs as a probe to detect Cr(VI) based on the inner filter effect (IFE) and dopamine based on the redox reaction, and the linear ranges were 0.25–243 μM for detection of Cr(VI) and 1.4–260 μM for detection of dopamine (DA), respectively. Moreover, this probe was utilized to analysis of dopamine in serum and urine samples, which was presaged more opportunities for application in biological field.

A novel fluorescence “turn on-off” method for sensitive and selective detection of heparin and heparinase I was developed based on near infrared Polyethyleneimine Capped Ag2S Quantum Dots (PEI-Ag2S QDs). The fluorescence “turn-on” arose from aggregation-induced emission enhancement (AIEE) characteristics of PEI-Ag2SQDs induced by electrostatic interaction between PEI-Ag2SQDs and heparin. Heparinase I, which can specifically hydrolyze heparin into short fragments would de-aggregate PEI-Ag2S QDs/heparin system and lead to fluorescence “turn-off”. Under optimal conditions described, the fluorescence enhancement at 685 nm was linearly related to the concentration of heparin and heparinase I in the range of 0.069–2.275 μM and 0–103 ng mL−1 with the relative correlation coefficient of R2 = 0.997 and 0.99 and detection limit as low as 6 nM and 0.5 ng mL−1, respectively. The activity of the heparinase I was further investigated using steady-state kinetic for the reaction. In ddition, the proposed method was successfully utilized in serum samples, which presaged more opportunities for application in related biochemical and biomedical researches.

In this work, we developed a ''naked-eye'' colorimetric and ratiometric fluorescence probe for a very important biomarker of uric acid (UA). The method was based on the oxidation of UA by uricase to allantoin and hydrogen peroxide, and then o-Phenylenediamine (OPD) was oxidized to the yellow-colored 2,3-diaminophenazine (oxOPD) in the presence of horseradish peroxidase (HRP) and hydrogen peroxide. The fluorescence emission of glutathione functionalized Ti

A fluorometric and colorimetric dual-mode sensing platform based on graphitic carbon nitrite quantum dots (g-CNQDs) and Fe (II)-bathophenanthroline complex (BPS-Fe2+) was designed to the sensitive detection of nitrite (NO2−) in sausage and water. In this system, the fluorescence of g-CNQDs was quenched by BPS-Fe2+ complex due to the inner filter effect (IFE). When NO2− was present, Fe2+ was oxidized by nitrite to form BPS-Fe3+ complex with BPS, leading to the recovery of the fluorescence from g-CNQDs. Therefore, we constructed a “turn-off-on” fluorescence probe for detection of NO2−. Moreover, with the increase of NO2− concentration, the color of the solution changed from red to colorless, so the UV–vis measurements and on-site visual detection were realized. The method is capable of detecting NO2− in the concentration range of 2.32–34.8 μM with good selectivity and high sensitivity. In addition, the method has the potential to determine NO2− in water samples and sausage samples.

Nitrogen and chlorine dually-doped carbon dots (N,Cl-CDs) were hydrothermally prepared starting from 4-chloro-1,2-diaminobenzene and dopamine. The N,Cl-CDs exhibit strong orange fluorescence, with excitation/emission maxima at 420/570 nm and a relative high quantum yield (15%). The N,Cl-CDs were employed to detect acetylcholinesterase (AChE) activity and organophosphate pesticides (OPs) which are enzyme inhibitors. Acetylthiocholine is enzymatically split by AChE to produce thiocholine which triggers the decomposition of Ellmans’s reagent to form a yellow colored product (2-nitro-5-thiobenzoate anion). The product causes an inner filter effect (IEF) on the fluorescence of the N,Cl-CDs. Fluorescence decreases linearly in the 0.017 to 5.0 Unit·L−1 AChE activity range, and the detection limit is 2 mUnit·L−1. If organophosphates are present, the activity of AChE becomes increasingly blocked, and this leads to a less expressed IFE and an increasing recovery of fluorescence. This was used for the quantification of OPs. Response is linear in the 0.3–1000 μg·L−1 OP concentration range with a 30 ng·L−1 detection limit.

Titanium carbide quantum dots functionalized with ε-poly-L-lysine (PLL) were synthesized by sonication cutting and hydrothermal synthesis. The deprotonated Ti

A sensitive naked eye and ratio-fluorescence sensor for Curcumin (CCM) and hypochlorite (ClO-) determination based on copper nanoclusters (Cu NCs) was developed. The fluorescence of the Cu NCs can be quenched due to inner filter effect (IFE) between CCM and Cu NCs, and the ratio fluorescence probe was formed. After adding ClO- to Cu NCs-CCM system, the phenolic and methoxy groups of CCM were oxidized to quinones, then the fluorescence of CCM was quenched and the fluorescence of Cu NC was restored. Moreover, the continuous detection of CCM and ClO- is accompanied by the change of solution color. Therefore, CCM and ClO- semiquantitative visual and fluorescence dual channel detection were realized. The detection results show that the detection based on Cu NCs-CCM probe has a wide detection range (0–412 µM) and low detection limit (24 µM), and a good recovery rate is obtained in adulterated milk and tap water detection. Furthermore, smartphone was introduced for image digital colorimetric analysis through the acquisition, recognition and RGB data processing of solution colors, providing an effective scheme for the field rapid detection of hypochlorite.

Recently, carbon dots (CDs) have drawn extensive attention owing to their unique properties. While more and more research had been focusing on the exploration of CDs as fluorescence sensors, the blue or green fluorescence emission of CDs restricts further applications of CDs, particularly in the biology-relevant fields due to the commonly blue auto-fluorescence of biological matrix. Therefore, the preparation of CDs with strong emission at long wavelengths is highly desirable. For these situations, a facile, straightforward and extra-reductant needless method was established to fabricate silver-carbon dot nanohybrid with enhanced near-infrared fluorescence through metal-enhanced fluorescence (MEF). We applied the Ag-CD nanohybrid as a probe to detect antioxidants such as ascorbic acid in near-infrared window, and the probe possesses a linear range of 0.2–60 μM. More importantly, this sensor could not only function in aqueous solution, but also display well selective response in intricate biological fluids. In addition, an IMPLICATION logic gate was constructed based on the unique characteristics of Ag-CD nanohybrid which presages more opportunities for application in single and multiple biological sensing.

This paper proposed a simple and sensitive approach for detecting graphene oxide (GO) in a wide pH range in environmental water samples using fluorescent β-CD protected Cu NCs based on the hydrogen-bond interactions between GO and 6-SH-β-CD. The influences of dilution ratio and pH were investigated. We found that the fluorescence quenching efficiency of Cu NCs by GO remained almost the same under pH from 4 to 10, which benefitted the monitoring of GO under different pH conditions in real samples. The fluorescence quenching mechanism was also discussed. The fluorescence of β-CD protected Cu NCs could be quenched in the presence of GO with a lowest detection concentration of 0.1 mg·L-1 . Good linear correlations were obtained over the concentration range from 0 to 30 mg·L-1 at different pH values (pH = 4, pH = 7 and pH = 12). In addition, this method was successfully applied to the determination of GO in real samples which presents more opportunities for application in environmental and material sciences.

In this report, a novel one-step chemical reduction method was reported for synthesis of water-soluble and stable fluorescent glutathione-templated silver nanocluster (GSH-Ag NCs) with ascorbic acid as an environmental-friendly reducing agent. On the basis of an oxidoreduction-induced fluorescence quenching mechanism, the prepared GSH-Ag NCs found to act as a cheap, non-toxic and highly sensitive "turn-off" fluorophore for ascorbic acid (AA). Furthermore, the fluorescence of the fluorophore/AA system could be recovered through addition of arginine (Arg), which made the system function as a highly selective "turn-on" sensor for arginine. Therefore, a "turn-off-on" switch sensor was proposed for detection of AA and Arg. Under optimized conditions, the probe gives a fluorescent response that is linear in the 2-300 μM concentration range of AA, with a detection limit of 0.1 μM. The probe for Arg, in turn, has a linear range in the 10-180 μM concentration range, and the limit of detection is 0.5 μM. In addition, the developed method showed great accuracy when employed to detect AA and Arg in human urine and serum, which shows its great potential in biological molecular recognition applications.

A novel fluorescence method for sensitive and selective detection of phosphate was developed based on near infrared emission Ag2S QDs/ Metal − Organic Shell Composite via the deposition of metal-organic (zinc-nitrogen) coordination shell around Ag2S QDs . Under optimal conditions described, the fluorescence intensity of the composite was decreased at 685 nm in the presence of phosphate, which was linearly related to the concentration of phosphate in the range of 0. 7 to 4.2 μM and 11.2 to 88.2 μM with the relative correlation coefficient of R2 = 0.998 and 0.987 respectively and detection limit as low as 6 nM. In addition, the proposed method was successfully utilized in serum samples, tap water and Yangtze River water samples with the recoveries ranged from 94.76 to 100.86 %, which presaged more opportunities for application in related bioassay and water sample researches.

The authors describe a method for increasing the peroxidase-like catalytic properties of copper nanoclusters (Cu-NCs) that are used in non-enzymatic assays. The Cu-NCs were prepared by utilizing 6-thio-β-cyclodextrin as both the template and as effective modulators for increasing the peroxidase-like properties of the Cu-NCs. The β-CD-coated Cu-NCs have an average diameter of 2 nm, are stable in aqueous solutions, display strong fluorescence with excitation/emission peak wavelengths of 360/450 nm, and possess peroxidase-like catalytic activity which makes them a useful enzyme mimic. We have applied the findings to non-enzymatic photometric determination (at 650 nm) of (a) H2O2 in the concentration range of 0.02 to 10 mM using the β-CD/Cu-NC assisted oxidation of tetramethylbenzidine by H2O2, and (b) glucose in the concentration range of 0.04 to 20 mM after addition of glucose oxidase and formation of H2O2. The detection limits (at an S/N ratio of 3) are 0.2 μM for H2O2 and 0.4 μM for glucose. The β-CD coating is found to result in a strong increase in the reaction rate, probably because the cavity of β-CD acts as a pocket for the recognition and catalysis of substrate. Hence, the binding specificity becomes similar to that of natural enzymes.

A rapid method is described for synthesis of copper nanoclusters (CuNCs) by utilizing L-histidine as the stabilizer and ascorbic acid (AA) as the reductant. The CuNCs display blue-green fluorescence with excitation/emission peaks at 390/485 nm. A sensitive fluorometric assay was worked out for determination of alkaline phosphatase (ALP) activity. If the ALP substrate p-nitrophenylphosphate (PNPP) is enzymatically hydrolyzed, it forms p-nitrophenol (PNP) which reduces the fluorescence of CuNCs because its absorption band at 410 nm overlaps the excitation peak of CuNCs at 390 nm. In addition, the amino groups and imidazole groups on the surface of CuNCs possibly form a complex with the phenol groups of PNP. This induces aggregation-induced quenching of the fluorescence of CuNCs. The fluorescent probe has a linear analytical range that extends from 0.5 mU·mL−1 to 40 mU·mL−1 and a detection limit of 45 μU·mL−1.

Stable copper nanoclusters (CuNCs) were prepared by utilizing D-penicillamine as both the stabilizer and reductant. The emission of the CuNCs (with excitation/emission peaks at 390/645 nm) is largely stabilized by coating with poly(sodium-p-styrenesulfonate) (PSS). Cytochrome c (Cyt c) quenches the fluorescence of the PSS-coated CuNCs, and this effect was exploited to design a quenchometric fluorometric assay for Cyt c. If trypsin is added to the loaded CuNCs, it will hydrolyze Cyt c to form peptide fragments, and fluorescence is gradually restored. A highly sensitive and fluorometric turn-off-on assay was constructed for sequential detection of Cyt c and trypsin. The linear ranges for Cyt c and trypsin are from 8.0 nM to 680 nM, and from 0.1 to 6.0 μg mL−1, and the lower detection limits are 0.83 nM and 20 ng mL−1 for Cyt c and trypsin, respectively.

A composite (Ag-g-CNQDs) was prepared from graphitic carbon nitride quantum dots and silver nanoparticles by water phase synthesis. Aided by metal-enhanced fluorescence, the composite exhibits excitation-dependent red emission with a peak at 600 nm with a quantum yield of 21%. If the composite is coated with polyethylenimine (PEI) to form the Ag-g-CNQD/PEI complexe, fluorescence is strongly reduced. Upon addition of heparin, the fluorescence of the system is enhanced because PEI has a higher affinity for heparin than Ag-g-CNQDs. The effect was used to design a fluorometric assay for heparin. The emission at 600 nm increases linearly in the 0.025 to 2.5 μM heparin concentration range, with a 8.2 nM limit of detection.

A composite (Ag-g-CNQDs) was prepared from graphitic carbon nitride quantum dots and silver nanoparticles by water phase synthesis. Aided by metal-enhanced fluorescence, the composite exhibits excitation-dependent red emission with a peak at 600 nm with a quantum yield of 21%. If the composite is coated with polyethylenimine (PEI) to form the Ag-g-CNQD/PEI complexe, fluorescence is strongly reduced. Upon addition of heparin, the fluorescence of the system is enhanced because PEI has a higher affinity for heparin than Ag-g-CNQDs. The effect was used to design a fluorometric assay for heparin. The emission at 600 nm increases linearly in the 0.025 to 2.5 μM heparin concentration range, with a 8.2 nM limit of detection. Graphical abstract Schematic illustration for fabricating a composite consisting of silver nanoparticles and graphitic carbon nitride quantum dots (Ag-g-CNQDs). Its red fluorescence is weak in presence of polyethyleneimine but restored on addition of heparin. This forms the basis for a new method for heparin detection.

We describe a kind of molecularly imprinted polymer (MIP)-based fluorescent sensor. It was obtained by anchoring a surface-imprinted MIP layer for the model analyte bisphenol A (BPA) onto the surface of fluorescent silver nanoclusters (Ag-NCs). The MIP-coated Ag-NCs were synthesized by the sol-gel technique. The hyphenation of the fluorescence of Ag-NCs with MIP technology expands the use of fluorescent nanomaterials in sensing and recognition. BPA is capable of quenching the fluorescence of the Ag-NCs, and the reduction in fluorescence intensity is related to the concentration of BPA in the 0.2 μg mL−1 to 2 mg L−1 range. The detection limit for BPA is 0.02 μg mL−1, and the recovery of BPA from spiked milk and juice samples ranged from 92.5 to 108.5 %. The MIP-coated Ag-NCs presented here are characterized by their ease of synthesis, selectivity and sensitivity. In our perception, this approach can be extended to numerous other analytes.

Graphene/silica magnetic nanocomposites are synthesised and introduced as new and reusable adsorbents for rapid and high-efficiency preconcentraton trace amounts of dye pollutants in water. This method is simple, fast, cheap and non-toxic. The optimum adsorption conditions for the preconcentraton of crystal violet (CV) and malachite green (MG) are investigated and the adsorption mechanisms are also discussed. The regeneration and reuse experiments showed the good reusability of the as-prepared adsorbent. In addition, this method was successfully applied to the preconcentraton of trace amounts of MG and CV from water samples, which presages more opportunities for application in environmental and material sciences.

Hexamethylene-1,3-bis(cetyldimethylammonium bromide) (G16-6-16) protected low-toxicity ZnSe quantum dots (QDs) were successfully synthesised and used as fluorescence probe to detect proteins such as bovine serum albumin (BSA). This method is simple, fast, selective and sensitive. Surfactant G16-6-16 can interact with proteins through hydrophobic effect, thus leading to the fluorescence quenching of G16-6-16 protected ZnSe QDs nanometre material. The fluorescence intensity of G16-6-16 protected ZnSe QDs was linearly proportional to BSA over a concentration range from 0 to 80 nM with a correlation coefficient of 0.993. The detection limit was 0.04 nM. This method was successfully applied to determine BSA in urine samples which shows the good application value of this nanometre material.

A series of self-nitrogen-doped and Zn-doped TiO2/C@SiO2 (ZTRH) nanoporous composites with high surface area and excellent biological hierarchical porous structure have been synthesized by sol–gel method at different temperatures. The porous SiO2 and activated carbon from the decomposition of rice husk (RH) were regarded as the template and porous catalytic carrier. The structure, crystallinity, morphology, and other physical–chemical properties of the samples were characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transforminfrared spectroscopy, N2 adsorption–desorption isotherms, and UV–vis diffuse reflectance spectroscopy. The feasibility of ZTRH nanoporous composites for decomposing pollutants was evaluated by rhodamine B under visible light irradiation. Compared with the traditional photocatalytic materials, ZTRH nanoporous materials not only performed high efficiency in pollutants degradation, but also exhibited good adsorption prop...

A versatile Zn-TiO2/RH/Fe3O4 ternary composite material on the basis of rice hull was prepared and characterized by X-ray diffraction, Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy, energy dispersive X-ray spectroscopy, and vibrating sample magnetometer analysis. Its ability to photocatalytically remove Rhodamine B (RhB) in wastewater was investigated in a photochemical reactor by means of ultraviolet and visible spectrophotometry and FT-IR. Research results show that the catalytic degradation rate of RhB from aqueous solution is close to 100% when using synthesized Zn-TiO2/RH/Fe3O4 as a catalyst under irradiation of visible light for 120 min. The as-prepared visible light-driven photocatalyst Zn-TiO2/RH/Fe3O4 material has high performance with excellent recyclability, magnetic separation feature, and photocatalysis activity in wastewater treatment.